In manufacturing electronic devices, dopants or impurities are introduced into a substrate to alter the substrate's original mechanical, optical, or electrical property. In manufacturing memory devices, boron ions may be introduced into a silicon substrate. As boron ions and silicon atoms in the crystal lattice have different electrical property, introduction of sufficient amount of boron ions may alter the electrical property of the silicon substrate.
Ion implantation technique may be used to introduce the dopants. In this technique, feed material containing desired species is ionized. Thereafter, the ions of the feed material are directed, in a form of an ion beam having desired energy, toward the substrate and thereafter implanted. If the ions are of different species, the ion may alter the property of the substrate.
A solar cell, another silicon substrate based device, may also be manufactured by introducing ions or dopants into the silicon substrate. In the past, the dopants have been introduced via diffusion process where dopant containing glass or paste is disposed on the silicon substrate. Thereafter, the substrate is heated, and the dopants in the glass or past are diffused into the substrate via thermal diffusion.
Although the diffusion process may be cost effective, the process has many drawbacks. In some solar cells, it is desirable to perform selective doping to introduce dopants to only selected region of the substrate. However, the diffusion process is difficult to control, and selective doping via diffusion may be difficult to achieve. The process may result in imprecise doping or formation of non-uniform doped regions. In addition, voids or air bubbles, or other contaminants may be introduced into the substrate along with the dopants during the diffusion process.
To address such drawbacks, doping via ion implantation process has been proposed. In the proposed process, the substrate is coated with photo-resist layer, and lithographic process is performed to expose portions of the substrate. Thereafter, the ion implantation is performed, and dopants are implanted into the exposed portions. The process, although achieves precise selective doping, is not inexpensive. Additional steps and time to coat, pattern, and remove the photo-resist, each of which adds costs to the manufacturing process, are required. The steps may be more complicated if the regions to be exposed are extremely small.
Any added cost in manufacturing the solar cell would decrease the solar cell's ability to generate low cost energy. Meanwhile, any reduced cost in manufacturing high-performance solar cells with high efficiency would have a positive impact on the implementation of solar cells worldwide. This will enable the wider availability and adoption of clean energy technology.
As such, a new technique is needed.